1. Field of the Invention
The present invention relates to an image processing device and a recording medium.
2. Description of the Related Art
If fog, mist, yellow sand, or PM2.5 occurs when the object, which is the capturing target, outside or at a long distance is captured and observed by a vehicle-mounted camera, monitoring camera, or electronic binoculars, light is scattered and the transmission rate is decreased. As a result, with regard to the object image, the contrast (the difference between light and dark) is reduced, and the visibility is deteriorated.
In order to improve the contrast, there is a conventionally-known technology for dividing an image into areas in accordance with its texture and equalizing the histogram with respect to the divided areas. This technology is called Contrast Limited Adaptive Histogram Equalization (CLAHE) and, during the CLAHE, the restriction is applied to the degree of the contrast enhancement.
For example, Japanese Unexamined Patent Application Publication No. 2006-195651 discloses a gradation correction device with which, in order to prevent excessive correction on background areas, the object, such as face or person, is detected, the restriction on the contrast of the face or person is reduced, and the restriction on the contrast of the others, such as background area, is increased.
Furthermore, when a camera or electronic binoculars is used with hand, if vibration occurs due to camera shake, wind, or the like, the visibility is deteriorated.
In order to improve the visibility against vibrations, there is a conventionally-known optical vibration control technology for reducing shake by detecting the direction of the shake and shifting the lens; or an electronic (image processing) type vibration control technology with which the direction of shake is detected based on the image captured by the camera, and the image is shifted corresponding to the shake.
It is considered that, to improve the visibility with cameras or electronic binoculars, both the vibration control processing and the area-division type enhancement processing, such as CLAHE, are performed in combination.
However, during processing, such as CLAHE, to correct the contrast intensity in accordance with the feature value of each area, the feature value of an area in the peripheral section of the image is different for each frame due to the vibration control, and therefore the correction amount for the contrast intensity is also different for each frame.
The gradation correction device, disclosed in Japanese Unexamined Patent Application Publication No. 2006-195651, has a problem in that while a continuous image, on which both the processes have been conducted, is viewed, flickering occurs in the peripheral section of the image and the visibility is deteriorated, and it is difficult to improve the visibility of images.